Field of the Disclosure
Embodiments of the present disclosure relate to a vehicle seat in which a seatback is partially allowed to swivel in accordance with a twisting motion of the occupant during turning of a vehicle.
Discussion of the Related Art
One example of the vehicle seat of this kind in which a backrest section is allowed to swivel with respect to a seatback frame is described in US2015/0367756 A1.
According to the teachings of US2015/0367756 A1, the backrest section is suspended from an upper portion of the seatback frame through a suspension section including a vertical-cord portion and a cross-cord portion. The vertical-cord portion and the cross-cord portion are configured by flexible and extendible/contractible linear shaped members. An outer periphery support section of the backrest is connected to the seatback frame through longitudinal wires at each width end portion and a width center of a lower end portion. In the vehicle seat taught by US2015/0367756 A1, therefore, the backrest section is allowed to swivel within flexibilities of the longitudinal wires around a swivel center situated at a level of thoracic vertebra of an occupant.
PCT international publication WO 2013/021497 also describes the vehicle seat in which a backrest is attached to the seat frame is allowed to rotate in the roll direction.
According to the teachings of US2015/0367756 A1, the backrest section may be allowed to swivel by the above-explained simple structure. In the vehicle seat taught by US2015/0367756 A1, however, the backrest section is allowed to swivel not only in the width direction but also in other directions with respect to the seatback frame. That is, in the vehicle seat taught by US2015/0367756 A1, the backrest section may be moved unnecessarily in an undesirable direction by any motion of the occupant.